Alert when door is open for X minutes?

If you have access to RBoy Apps, use this SmartApp:

Under Door Open/Close actions you can enable to option to Notify you if the door is left open for X minutes (you can set individual times for each door or a one time for all doors).

It works with the STSC (new) and the Classic app. However you’ll need the Classic app to install the app initially since the STSC doesn’t support installation of custom apps as yet. Once installed it’ll show up under Automations in both apps.